Magnetic Devices Optical Devices

Sequential Access Direct Access CD-ROM

Magnetic Tape Magnetic Disk

Floppy Disk Hard Disk

Tracks – For data recording the surface of a disk is divided into a number of invisible concentric circles called as tracks.

Sectors – Each track is further subdivided into sectors, a sector is the

smallest unit of data access from a disk. Floppy Disk

• Floppy disks are so called

because they are made of flexible plastic plates, which can bend, not hard plates.• They are also known as floppies or diskettes.• They were introduced by IBM in 1972, and are now being produced in various sizes and capacities by many manufacturers. Tracks and Sectors

The disk is divided into

tracks (brown) andsectors (yellow). Floppy Disk Drive

• A floppy-disk drive is a device, which is used to

read/write data from/to floppy disks.• The drive has a spindle, which rotates the disk, and the read/write heads, which can move in and out to position the read/write heads on any track of the disk surface.• It is of the interchangeable magnetic disk type. That is it allows loading and unloading of magnetic disks, as and when they are needed, for reading/writing data on them. 3½ -inch floppy disk All 3½ floppy disks are of double-sided type, and record data on both the disk surfaces. However they come in three different capacities –• Double density 3½ inch diskettes have 40 tracks, 18 sectors/track, and 512 bytes/sector – total storage capacity 720 KB (approximately).• The high density 3½ inch diskettes have 80 tracks, 18 sectors/track, and 512 bytes/sector – total storage capacity 1.4 MB (approximately).• The very high density 3½ inch diskettes have 80 tracks, 36 sectors/track, and 512 bytes/sector – total storage capacity 2.88 MB(approximately). Floppy Disk

Advantages – 1. Low Cost

2. Easy to Carry away.

Disadvantages – 1. Less durability

2. Low capacity for

storage Hard disk basics

• Hard disks were invented in the 1950s.

• They started as large disks up to 20 inches in diameter holding just a few megabytes.• They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product).• They later became known as "hard disks" to distinguish them from "floppy disks."• Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies. Capacity and Performance

• Capacity of the drive - the number of bytes it can hold.-

10 and 40 gigabytes.• Data rate - The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common.Access time on Disk• Seek time : Time to position the head on a specific track.• Latency time : The time required by a sector to reach below the read/write head.• Disk Access time : Is considered to be sum of seek time and latency time. Storing the data• Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track.• A typical track is shown in yellow; a typical sector is shown in blue.• A sector contains a fixed number of bytes -- for example, 256 or 512. Hard-disk drive

• It is a sealed aluminum box with controller electronics attached to one side Electronics Board• The electronics control the read/write mechanism and the motor that spins the platters.• The electronics also assemble the magnetic domains on the drive into bytes (reading) and turn bytes into magnetic domains (writing). Platters & Arm Removing the cover from the drive reveals an extremely simple but very precise interior

• The platters - These

typically spin at 3,600 or 7,200 rpm when the drive is operating.

• The arm - This holds the

read/write heads and is controlled by the mechanism in the upper-left corner. Multiple Platters

• In order to increase the

amount of information the drive can store, most hard disks have multiple platters. This drive has three platters and six read/write heads: Hard Disk

Advantages – Disadvantages -

1. More Capacity 1. Difficult to carry away

2. More Durable 2. Costly

3. Faster Access Magnetic: Zip – In this type, a single disk platter is encased in a plastic cartridge. – Commonly used zip disk is of 3½ inch size, having storage capacity of 100 MB, depending upon the formatting style used by a particular computer system. – Its disk drive is called a zip drive.• Storage Capacity- up to 750 MB at the moment. Magnetic: Cartridges• Each Jaz cartridge is basically a hard disk, with several platters, contained in a hard, plastic case.• The cartridge contains neither the heads nor the motor for spinning the disk; both of these items are in the drive unit.• The current Jaz drive uses 2- GB cartridges, but also accepts the 1-GB cartridge used by the original Jaz. Magnetic: Portable Drives• Completely external, portable hard drives are quickly becoming popular, due in a great part to USB technology.• These units, like the ones inside a typical PC, have the drive mechanism and the media all in one sealed case.• The drive connects to the PC via USB cable and, after the driver software is installed the first time, is automatically listed by Windows as an available drive.• This 20-GB Pockey Drive fits in the palm of your hand. Magnetic Tape Magnetic tapes are mounted on reels or a cartridge or a cassette of tape to store large volumes or backup data. The tape drive is termed as sequential access drive. The tapes are one of the earliest storage devices.

 They are low cost, low speed, portable and are still widely used because of their low cost. Used for Backup Storage

 Slower Access Solid-state Storage

 A very popular type of removable storage for small

devices, such as digital cameras and PDAs, is Flash memory.

 Flash memory is a type of solid-state technology, which

basically means that there are no moving parts

 Flash memory is an erasable memory chip.

Solid-state Storage Devices• Flash-memory storage devices such as CompactFlash or SmartMedia cards are today's most common form of electronic nonvolatile memory.• This SmartMedia card holds 64 MB. Solid-state Storage Devices